A summary of carb, protein and fat metabolism for bodybuilders

[Saurus]

I've noticed quite a few questions on M&S lately such as: "Can Proteins be stored as fat?", "Should I take protein before or after cardio?" etc, so I decided to drag up an old unfinished 'article' that I was writing for M&S, and decided to post it here. (As a biochemist, this was one of my fields of study.)

OK, here's a simplified version of Carb, Protein and Fat metabolism as it relates to bodybuilding...

As you eat, the following happens:

1. Digestion starts immediately in the mouth, where the amylase enzyme starts breaking down starch into glucose. Simple carbs are converted to glucose almost immediately after they are eaten. Complex carbs first need to be broken down into simple carbs before they are converted to energy. Glucose is converted to energy in the form of ATP, as your body requires.

2. After you have met your immediate energy requirements, your body's next priority is to replenish glycogen stores. Glycogen is a way of storing glucose where it can be made immediately available in the case of exertion, such as sprinting or lifting heavy weights, or endurance exercise. Insulin stimulates the action of the glycogen producing enzyme, glycogen synthase.

3. Protein is first broken down into short chains of amino acids by the enzyme pepsin, and then into single amino acids by pancreatic enzymes such as trypsin. Amino acids cannot be stored in the body, and will form an "amino acid pool" in the body, which can be drawn from when muscle synthesis is required, or when glycogen stores are depleted. Once the 'amino acid pool' is full, excess amino acids get converted to sugars (carbs) and fatty acids.

4. Once glycogen stores are depleted, your body will use up the 'amino acid pool' as fuel before turning to fats. This is why you should do cardio on an empty stomach if your goal is to lose weight - so that both the glycogen stores and amino acid pool are quickly used up, forcing the body to turn to fat for fuel. Also, this is why you should not do cardio if your goal is to build muscle mass, since this amino acid pool will then be used up as fuel, and will no longer be available to draw amino acids from for muscle building.

5. Once all available glucose, glycogen, and free amino acids are used up, your body will start using fat as a fuel.

6. If there is an excess of carbs, these will be converted to fat as soon as the glycogen stores are full (roughly 30-40 minutes after eating). An excess of protein depends on your total protein consumption during the day, and is independent of the amount of carbs/fat consumed, but will depend on your amino acid pool as described above.

(An interesting consequence of this is that if your amino acid pool is full, every gram of protein you eat will turn to fat. Conversely, if your amino acid pool is being used up faster than you can refill it, no matter what your daily calories, you could eat almost unlimited (pure) protein without putting on a single gram of fat from it.) - This is also why it is important to eat your protein in many small meals during the day! Your body cannot normally handle more than 25-40g of protein at a time, and will convert the rest to sugars and fatty acids, whereas eating it spread out over the day will give you a non-fattening, endless source of amino acids for your muscle building!

7. Fats which you eat are broken down mainly into fatty acids, which are stored as fat, but also as glycerol, which is used to help break down glucose into energy. Thus, too much dietary fat will result in fat storage. Too little fat will result in too little glycerol, resulting in inefficient glycolysis (carb digestion), which will mean your body will use other recources such as muscle for fuel, something you most definitely don't want.


In reality, all of the above are slightly more complex, but this is sufficient to give you a good undertanding of what happens, and should give you an idea of how and when to eat and exercise. ie
- eat many small, balanced (carbs, protein, fats) meals in a day
- to lose fat, do cardio on an empty stomach.
- don't do cardio or endurance exercises if your sole goal is to build muscle mass
- eat enough fats, but not too much.
- eat enough protein, but spread it out!!!

[LtL]

Originally Posted by Saurus

I've noticed quite a few questions on M&S lately such as: "Can Proteins be stored as fat?", "Should I take protein before or after cardio?" etc, so I decided to drag up an old unfinished 'article' that I was writing for M&S, and decided to post it here. (As a biochemist, this was one of my fields of study.)

OK, here's a simplified version of Carb, Protein and Fat metabolism as it relates to bodybuilding...

As you eat, the following happens:

1. Digestion starts immediately in the mouth, where the amylase enzyme starts breaking down starch into glucose. Simple carbs are converted to glucose almost immediately after they are eaten. Complex carbs first need to be broken down into simple carbs before they are converted to energy. Glucose is converted to energy in the form of ATP, as your body requires.

2. After you have met your immediate energy requirements, your body's next priority is to replenish glycogen stores. Glycogen is a way of storing glucose where it can be made immediately available in the case of exertion, such as sprinting or lifting heavy weights, or endurance exercise. Insulin stimulates the action of the glycogen producing enzyme, glycogen synthase.

3. Protein is first broken down into short chains of amino acids by the enzyme pepsin, and then into single amino acids by pancreatic enzymes such as trypsin. Amino acids cannot be stored in the body, and will form an "amino acid pool" in the body, which can be drawn from when muscle synthesis is required, or when glycogen stores are depleted. Once the 'amino acid pool' is full, excess amino acids get converted to sugars (carbs) and fatty acids.

4. Once glycogen stores are depleted, your body will use up the 'amino acid pool' as fuel before turning to fats. This is why you should do cardio on an empty stomach if your goal is to lose weight - so that both the glycogen stores and amino acid pool are quickly used up, forcing the body to turn to fat for fuel. Also, this is why you should not do cardio if your goal is to build muscle mass, since this amino acid pool will then be used up as fuel, and will no longer be available to draw amino acids from for muscle building.

5. Once all available glucose, glycogen, and free amino acids are used up, your body will start using fat as a fuel.

6. If there is an excess of carbs, these will be converted to fat as soon as the glycogen stores are full (roughly 30-40 minutes after eating). An excess of protein depends on your total protein consumption during the day, and is independent of the amount of carbs/fat consumed, but will depend on your amino acid pool as described above.

(An interesting consequence of this is that if your amino acid pool is full, every gram of protein you eat will turn to fat. Conversely, if your amino acid pool is being used up faster than you can refill it, no matter what your daily calories, you could eat almost unlimited (pure) protein without putting on a single gram of fat from it.) - This is also why it is important to eat your protein in many small meals during the day! Your body cannot normally handle more than 25-40g of protein at a time, and will convert the rest to sugars and fatty acids, whereas eating it spread out over the day will give you a non-fattening, endless source of amino acids for your muscle building!

7. Fats which you eat are broken down mainly into fatty acids, which are stored as fat, but also as glycerol, which is used to help break down glucose into energy. Thus, too much dietary fat will result in fat storage. Too little fat will result in too little glycerol, resulting in inefficient glycolysis (carb digestion), which will mean your body will use other recources such as muscle for fuel, something you most definitely don't want.


In reality, all of the above are slightly more complex, but this is sufficient to give you a good undertanding of what happens, and should give you an idea of how and when to eat and exercise. ie
- eat many small, balanced (carbs, protein, fats) meals in a day
- to lose fat, do cardio on an empty stomach.
- don't do cardio or endurance exercises if your sole goal is to build muscle mass
- eat enough fats, but not too much.
- eat enough protein, but spread it out!!!

Consider yourself repped. Great post!

LtL

[BolanRox]

great post mate!

[Quiff81]

great post .

Rep + for you buddy



Q.

[Shoalpt]

REP from me as well. I will post a Q that you might have an answer to.

[Doug]

Rep + from me as well,

[recently93]

Originally Posted by Saurus

I've noticed quite a few questions on M&S lately such as: "Can Proteins be stored as fat?", "Should I take protein before or after cardio?" etc, so I decided to drag up an old unfinished 'article' that I was writing for M&S, and decided to post it here. (As a biochemist, this was one of my fields of study.)

OK, here's a simplified version of Carb, Protein and Fat metabolism as it relates to bodybuilding...

As you eat, the following happens:

1. Digestion starts immediately in the mouth, where the amylase enzyme starts breaking down starch into glucose. Simple carbs are converted to glucose almost immediately after they are eaten. Complex carbs first need to be broken down into simple carbs before they are converted to energy. Glucose is converted to energy in the form of ATP, as your body requires.

2. After you have met your immediate energy requirements, your body's next priority is to replenish glycogen stores. Glycogen is a way of storing glucose where it can be made immediately available in the case of exertion, such as sprinting or lifting heavy weights, or endurance exercise. Insulin stimulates the action of the glycogen producing enzyme, glycogen synthase.

3. Protein is first broken down into short chains of amino acids by the enzyme pepsin, and then into single amino acids by pancreatic enzymes such as trypsin. Amino acids cannot be stored in the body, and will form an "amino acid pool" in the body, which can be drawn from when muscle synthesis is required, or when glycogen stores are depleted. Once the 'amino acid pool' is full, excess amino acids get converted to sugars (carbs) and fatty acids.

4. Once glycogen stores are depleted, your body will use up the 'amino acid pool' as fuel before turning to fats. This is why you should do cardio on an empty stomach if your goal is to lose weight - so that both the glycogen stores and amino acid pool are quickly used up, forcing the body to turn to fat for fuel. Also, this is why you should not do cardio if your goal is to build muscle mass, since this amino acid pool will then be used up as fuel, and will no longer be available to draw amino acids from for muscle building.

5. Once all available glucose, glycogen, and free amino acids are used up, your body will start using fat as a fuel.

6. If there is an excess of carbs, these will be converted to fat as soon as the glycogen stores are full (roughly 30-40 minutes after eating). An excess of protein depends on your total protein consumption during the day, and is independent of the amount of carbs/fat consumed, but will depend on your amino acid pool as described above.

(An interesting consequence of this is that if your amino acid pool is full, every gram of protein you eat will turn to fat. Conversely, if your amino acid pool is being used up faster than you can refill it, no matter what your daily calories, you could eat almost unlimited (pure) protein without putting on a single gram of fat from it.) - This is also why it is important to eat your protein in many small meals during the day! Your body cannot normally handle more than 25-40g of protein at a time, and will convert the rest to sugars and fatty acids, whereas eating it spread out over the day will give you a non-fattening, endless source of amino acids for your muscle building!

7. Fats which you eat are broken down mainly into fatty acids, which are stored as fat, but also as glycerol, which is used to help break down glucose into energy. Thus, too much dietary fat will result in fat storage. Too little fat will result in too little glycerol, resulting in inefficient glycolysis (carb digestion), which will mean your body will use other recources such as muscle for fuel, something you most definitely don't want.


In reality, all of the above are slightly more complex, but this is sufficient to give you a good undertanding of what happens, and should give you an idea of how and when to eat and exercise. ie
- eat many small, balanced (carbs, protein, fats) meals in a day
- to lose fat, do cardio on an empty stomach.
- don't do cardio or endurance exercises if your sole goal is to build muscle mass
- eat enough fats, but not too much.
- eat enough protein, but spread it out!!!

First of all, great post. The only thing i was wondering about is you say to do cardio on an empty stomach to loose more fat, but this article (http://www.muscleandstrength.com/art...yths.html)says that exercising on an empty stomach doesnt actually burn more fat.

[Doug]

Originally Posted by recently93

First of all, great post. The only thing i was wondering about is you say to do cardio on an empty stomach to loose more fat, but this article (http://www.muscleandstrength.com/art...yths.html)says that exercising on an empty stomach doesnt actually burn more fat.

Peforming low intensity cardio first thing in the morning before breakfast is a great time for using fat for fuel as you will be partly glcogen depleted from sleeping during the night.

[recently93]

Originally Posted by Doug

Peforming low intensity cardio first thing in the morning before breakfast is a great time for using fat for fuel as you will be partly glcogen depleted from sleeping during the night.

so to clarify, doing cardio on an empty stomach does help burn more fat?

[darshan]

Originally Posted by recently93

so to clarify, doing cardio on an empty stomach does help burn more fat?

Potentially given the right environment (intensity, duration, etc).

For most regular folk, the effects of fasted cardio are not exactly profound enough to make a scheduling change.

For very lean individuals trying to get rid of the last bit of stubborn fat, it could potentially make a difference.